"Database connection."

Hi,

I am trying to connect RapidMiner with SQL server using sql server Authentication.But am not able to connect with database and always getting a message " Database error occurred: The TCP/IP connection to the host has failed. java.net.ConnectException: Connection refused: connect ".I have already enabled the driver in RM.This is my process.

<operator name="Root" class="Process" expanded="yes">
    <operator name="DatabaseExampleSource" class="DatabaseExampleSource">
        <parameter key="database_system" value="Microsoft SQL Server (Microsoft)"/>
        <parameter key="database_url" value="jdbc:sqlserver://computer-647;databaseName=DataMart"/>
        <parameter key="username" value="sa"/>
        <parameter key="password" value="VNfe8QITNRw19hgf6f6UpA=="/>
        <parameter key="query" value="select * from F_TFQ"/>
    </operator>
</operator>

Thanks
Ratheesan